Thermoresponsive snap action switch



'June 13, 1961 R. J. cAsslDY 2,988,621

' THERMoREsPoNsIvE SNAP ACTION swITcH Filed .my 2a, 1959 .IEl-l- 5g;

INVENTORZ 05252 J.' 245511722 s ATTORNEY z United States Patent O 2,988,621 THERMORESPONSIVE SNAP ACTION SWITCH Robert J. Cassidy, Greenville, S.C., assignor to Pace, Inc., Mansfield, Ohio, a corporation of Ohio Filed July 28, '1959, Ser. No. 830,023 6 Claims. (Cl. 200--138) This invention relates to thermoresponsive or thermostat switch means of the snap action type and more especially to a thermoresponsive snap action switch construction provided with manual control adjustable throughout an effective operating temperature range of the switch construction.

Control switches have been utilized embodying a thermoresponsive means or thermostat to maintain automatic control of a predetermined temperature within a given temperature range embraced within a manual control, such devices having particular application in appliances embodying heating elements or electrically energizable means controllable within a desired temperature range. Such appliances in which switches of this character have been used include flat irons, grills, fry pans and other electrically energizable appliances. In most types of thermostat switches utilized for the above-mentioned purposes, a thermoresponsive means such as a bimetallic element movable under the influence of temperature changes is employed wherein the liexure of the thermoresponsive means directly controls the position of a contact arm of the switch mechanism to open or separate circuit completing contacts when the temperature is elevated above a predetermined setting of the switch mechanism and, upon cooling or reduction in temperature, flexes in the opposite direction to permit reengagement of the contacts.

In switches of this character, the action of the bimetallic element in its llexure under temperature change is comparatively slow in flexing the switch arm suiiiciently to engage or disengage the circuit completing contacts and a certain amount of arcing occurs across the contacts at the period of making and breaking of the contacts which deteriorates the contacts and impairs the sensitivity or accuracy of control.

The present invention embraces an arrangement of switch means embodying a snap action wherein movement of the thermoresponsive means is imparted to a resilient member until a point is attained wherein the potential energy in the resilient member is effective to nstantly engage or separate the contacts of the switch mechanism whereby arcing across the contacts is reduced to a Another object of the invention is the provision of a thermoresponsive switch means or thermostatically controlled switch embodying a thermoresponsive member arranged to influence the position of a movable switch arm through a resilient means whereby the circuit completing contacts of the switch mechanism may be engaged and disengaged by a snap action to more accurately maintain the temperature of an appliance or maintain the temperature of a region adapted to be controlled by electrically energized means.

Another object of the invention resides in a thermoresponsive switch mechanism embodying a thermoresponsive member or element arranged to influence the relative position of a movable switch arm in a manner whereby a high degree of sensitivity of temperature control is attained.

Another object of the invention is the provision of a thermostatically controlled snap action switch mechanism in which a thermoresponsive element influences the relative position of a movable contact carrying member through the intermediary of a resilient member of arcuate configuration whereby minute changes in temperature adjacent the thermoresponsive means are eiective to move the switch arm for making and breaking an electric circuit.

Still another object of the invention resides in a switch mechanism having relatively movable contact carrying members, one member being subject to manual control for predetermining the position thereof within a defined temperature range, the other being under the influence of a thermoresponsive means which is effective through a curved or arcuately shaped member to control the position of the thermostatically controlled switch arm to maintain a substantially constant temperature condition in the region of the thermoresponsive means.

Still a further object of the invention is the provision of a manually controllable, thermostat switch mechanism wherein the sensitivity of operation of the snap action of the thermally actuated switch arm may be adjusted whereby the mechanism is effective to maintain temperatures controlled by the switch mechanism within extremely small temperature variations.

Further objects and 'advantages are within the scope of this invention such as relate to the arrangement, operation and function of the related elements of the structure, to various details of construction and to combinations of parts, elements per se, and to economies of manufacture and numerous other features as will be apparent from a consideration of the specification and drawing of a form of the invention, which may be preferred, in which:

FIGURE l is an enlarged longitudinal sectional view through -a switch mechanism embodying the invention;

FIGURE 2 is a top plan View of the construction illustrated in FIGURE 1;

FIGURE 3 is a detail View of the manual control means providing manual adjustment for positioning one of the switch components;

FIGURE 4 is an enlarged detail sectional view taken substantially on the line 4-4 of FIGURE l;

FIGURE 5 is an enlarged detail sectional view taken substantially on the line 5 5 of FIGURE 1;

FIGURE 6 is an enlarged detail sectional view taken substantially on the line 6 6 of FIGURE 1, and

FIGURE 7 is an elevational view of the switch mechanism showing the relative positions of components of the mechanism when the contacts are in engaged relation.

The switch mechanism of the invention has been illustrated as adaptable for controlling the energization of a heating element, such as the heating element of an applitance, but it is to be understood that the switch mechanism of the invention also has particular utility in the exercise of accurate control of the circuits of air-conditioning equipment or refrigeration units and the utilization of the switch mechanism is contemplated in any arrangement Where it is desirable or essential to establish accurate temperature control of an appliance or of any region subjected to temperature variations.

Referring to the drawings in detail and particularly to FIGURES l, Zand 7, there is illustrated a portion 10 of an electrically heated or controlled appliance as, for example, an electric iron which is provided with a heating element or component illustrated diagrammatically at 12 to which electrical energy is supplied through supply conductors or power lines L-l and L-2. In the embodiment illustrated, the portion or plate 10 of the appliance is utilized as a mounting for the switch mechanism but any suitable mounting may be employed.

The switch construction in FIGURE 1 is illustrated as enlarged to about twice actual size and is inclusive of a frame or frame structure comprising `a plate 14 and a tubular member or sleeve 16, the plate 14 being formed with a suitable opening `to receive an end of the sleeve 16, the sleeve supporting several components of the switch assembly to form a stacked switch. A portion of the end of the sleeve is swaged or staked as at 1S to secure the sleeve and frame plate 14 in fixed relation. The switch mechanism Imay be secured to the plate 10 of the appliance by means of a bolt 20 and securing nut 21, the bolt extending through the sleeve and an opening in the plate 10 as shown in FIGURE l.

It is to be understood that the switch mechanism may be mounted by other suitable means depending upon the particular use or position of the switch means. The arrangement includes a manually adjustable means operable within the operating temperature range of the switch for manually adjusting the position of one of the switch arms or components in a position whereby a thermoresponsive means is thereafter effective to maintain the temperature constant for the value for which the manual means is adjusted.

In the embodiment illustrated, the plate 14 is provided with an opening to receive a projecting sleeve portion 22 of a fitting 24, the extremity 26 of the sleeve portion 22 being swaged or staked into engagement with the plate 14 to securely mount the fitting 24 on the plate. The appliance shown in FIGURE l is provided with a housing member 28 which is formed with an opening to receive a threaded portion 3i? of the fitting 24, a securing nut or sleeve 32 being in threaded engagement with the po-rtion 3i) to secure the fitting 24 and member 28 in fixed relation.

The interior of the sleeve or fitting 24 is threaded to receive the threaded portion 34 of a manually rotatable shaft 36, The shaft 36 is provided with a finger gip or knob 38 preferably formed of insulating material. The fitting 24 is provided with an upwardly extending abutment or projection 40 which is disposed in the path of a pin 42 carried by the knob or manually operable means 38 for defining the limits of `movement of the knob 38, the extent of rotation of the shaft 36 embracing the temperature range controllable by the switch.

The switch mechanism is inclusive of a first switch arm or member 44, the position of which is controlled by the manually rotatable shaft 36. A strut or member 46 formed of ceramic or lava is contained within a socket or recess formed in the lower end of the shaft 36. The lower end of the strut 46 engages the first switch member or arm 44 as shown in FIGURE l whereby rotation of the shaft 36 iiexes the switch arm 44 either upwardly or downwardly dependent upon the direction of rotation of the shaft 36 to predetermine the position of the arm 44 in accordance with a temperature to be maintained within the temperature range under control of the manipulating means 3S.

The first switch member or arm 44 is mounted upon an annular disk 48 formed of insulating material which surrounds the supporting sleeve 16. A terminal member 50 is in metallic contact with the switch -member 44 and is likewise insulatingly supported upon the supporting sleeve 16, the terminal member 50 being adapted to be connected to a current supply conductor or power line designated L-2 schematically illustrated in FIGURE 1.

The switch construction is inclusive of a second switch member or arm 52, an end region thereof being mounted upon a disk 58 of insulating material surrounding the supporting sleeve 16. The edges of the switch member 52 are formed with downwardly extending flanges 54 which terminate a short distance from its mounting on the insulating washer 58. Through this arrangement the iiexure of the second switch member 52 takes place in the manner of a hinging or pivoting action at the region adjacent the mounting as the flanged region is of more rigid character.

Disposed in substantial parallelism with the switch member 52 is a third arm or actuating member 64I. The third arm construction 60 as illustrated is inclusive of a component 62 which is mounted upon the annular disk S on the sleeve 16. Also surrounding the tenon portion of the insulating disk 58 is a washer or disk 64 of metal for the purpose of spacing the second and third arms 52 and 60 respectively at their mounting region on the sleeve 16 as illustrated in FIGURE l. Disposed in metallic contact with component 62 of the arm 6i) is a terminal member 66 which is connected to -an electrically energizable heater or other element 12 as shown schematically in FIGURE l.

The opposite end of the element l2 is connected to the current conductor or power line designated L-I. The arm 6u includes a second component 63 which is spot welded or otherwise secured to the component 62 of the arm 60. The first current conducting switch arm or member 44 is provided with a contact 7i), and the second arm 52 is provided with a contact 72, these contacts being arranged for cooperation to comple-te or interrupt a circuit through the heating element or other electrically energizable unit 12.

The arrangement of the invention includes a thermo responsive means or bimetallic member or element 74 having one end mounted upon the supporting sleeve 16 as illustrated in FIGURE l. The thermoresponsive means 74 is of a character which is iiexed or distorted rby variations in the ambient temperature and is arranged to move 0r iniiuence the position of the second switch arm 52 for engaging and disenga-ging the contacts 70 and 72 through the medium of a yieldable 4means providing a snap action of the switch member 52 from one position to the other.

As shown in FIGURE l the distal end of the component 68 of the third arm or actuating member 6@ extends upwardly as indicated at 76 `and terminates in a portion or projection 7S extending toward and spaced from the distal end of the second switch arm 52. Disposed between the projecting portion 73 of the comf ponent 68 of the actuating member 6I) and the `distal end of the second switch member or arm 52 is a fiexible or resilient element or spring Si) which, as shown in FIGURES l and 7, is of `semicircular or arcuate configuration.

The member Sii is formed as a strip of metal of spi-inglike character which in assembly as shown in FIGURE l is under stress between its regions of engagement with a projecting portion 78 of the actuating mem er 6i? and the distal end of the switch arm 52. By flexing the portion 68 of the actuating member 611i, the position of the projection 78 is changed and a toggle action or snap action is imparted to the switch member 52 through the arcuately shaped spring S0 as the spring exerts a biasing force on the switch member 52 in one direction or the other depending up n the relative position of the projection 78.

The spring Si) may be fashioned of a thin strip of metal such as spring steel, beryllium copper, brass or similar material, the end regions of the spring being provided with rectangularly shaped `apertures or openings I82 to receive respectively a tongue 84 provided at the end of the switch arm 52 and a similarly shaped tongue 86 formed onthe end region of projection 78 of the member 68. In assembled relation as shown in FIGURES 1, 2 and 7, the metal strip providing the spring is compressed or stressed into substantially a semicircular coniiguration or shape.

The distal end region of the thermoresponsive means or bimetallic element 74 is provided with a strut or member SS formed of insulating material such as ceramic or lava which is adapted, upon ilexure of the thermoresponsive means 74, in one direction to engage the portion 65 of the actuating member 60. Means is incorporated in the switch construction of the invention for regulating or controlling the relative sensitivity of the mechanism to provide snap action under minute thermal differentials effective to actuate the switch arm 52 from contact making or breaking position to an opposite position.

.As particularly shown in FIGURES l, 4 and 7, the distal end region of the switch member 44 is provided Vwith an opening to receive a tenon portion of a fitting 90, a portion 92 ofthe tenon being swaged over the lower surface of the switch member 44 as shown in FIGURE 4 to secure the fitting 90 to the switch member. The fitting 90 is formed with a threaded bore adapted to receive a threaded member 94 which is adjustable relative to the tting and the switch member 44, a suitable kerf 96 being provided in the upper end of member 94 to receive a suitable tool for adjusting purposes.

The lower end of the member 94 is formed with a recess or socket 98 adapted to receive one end of -a strut or member 100 formed of insulating material such as cetramic or lava. The lower end region 102 of the strut -100 seats in a slight depression or recess formed in the member 60 so as to prevent lateral displacement of the strut 100. The strut member 190 extends through la clearance opening 104 formed in the switch member 52 as shown in FIGURES 1 and 4.

By rotating the member 94 relative to the fitting 90 the distance between the regions of switch member 44 and the actuating member 60 adjacent the strut 100 may be regulated or varied. Such adjustment varies the spacing between the contacts 70 and 72 and the spacing directly affects the sensitivity of operation of the snap action mechanism. lFor example, if it is desired that the snap action of the spring 80 upon the switch arm 52 take place under a minute change in temperature ambient the thermoresponsive means 74, member 94 is adjusted to a position wherein the contacts 70 and 72 are just out of engagement.

It will be noted that movement of the arm or member 68 in one or the other directions to shift the projection 78 to one side or the other of a plane through the major surface of the switch member 52 sets up a biasing force through the spring 80 effective to move the switch arm 52 in one direction or the other. Assuming, for example, that the contacts are in closed position or circuit completing position as shown in FIGURE 7, the projection 78 is slightly below a plane through a major surface of the switch member 52.

As the temperature rises and influences the thermoreponsive means 74, the latter is ilexed upwardly as viewed in FIGURES 1 and 7 whereby the strut 88 on the thermoresponsive means engages Iand moves the distal end region of member 68 upwardly -to an intermediate or critical position at which no biasing force is transmitted to the switch arm 52 to cause an actuating movement or snap action of the switch arm.

Upon further slight upward movement of the thermoesponsive means 74, the portion 68 and projection 78 are elevated further to rock the spring 80 about the end of the switch arm as a fulcrum and through the critical position to establish a bias in the opposite direction against the switch arm 52 and this thrust action instantly and with a snap action moves the switch arm S2 downwardly as viewed in FIGURES l and 7 to instantly separate the contacts 70 and 72 as shown in FIGURE 1 and interrupt the circuit through the switch mechanism.

A biasing force effective to move the switch member 52 in `the opposite direction is set up upon cooling of the thermoresponsive -means 74. The thermoresponsive means is thus tiexed in the opposite direction and the strut 88 moved downwardly. 'Ihe member 68 is tensioned to follow the downward movement of the strut 88 until an over center position of projection 78 is attained, transferring the bias Iacting against the switch member 52 in an upward direction to again engage the contacts 70 and 72 and complete an energizing circuit.

lIt will be apparent that the relative movement of the arcuate spring 8G during actuation is slight and as the thrust action is borne by a substantial width of lthe spring engaging the actuating member and the switch member 52 being actuated, the wear upon the spring is negligible. Thus the spring 80 may be fashioned of a comparatively thin strip of metal to enhance or increase its sensitivity factor.

Through this arrangement an instantaneous make and break of the switch contacts is iattained and arcing between the contacts reduced to a minimum whereby the contacts are capable of long life and dependable operation. It should also be noted that the current flow through the switch arm 52 is directly through the contacts 70 and 72 to the switch arm 44 so that it is unnecessary for the current to flow through the spring 80, which is another factor facilitating the fabrication of the spring of an extremely thin strip of metal as its resistance to current flow is not involved in the functioning of the switch mechanism.

It should further be noted 4that the lateral edge regions of the switch arm 44 are provided with embossed or raised portions 168 which terminate at a point spaced from the mounting of the switch member by the insulating disk 48. The embossments 108 on the switch member 44 provide substantial rigidity in the region of the switch member between the point of engagement of the strut member 46 and the fitting 90. The adjusting movements of the manipulating knob 38 for manually positioning .the switch member 44 in a position corresponding to a temperature to be maintained by the automatic thermoresponsive means, cause tiexure of the switch arm ='44 at a region between the ends of the embossments l108' and the insulating disk y48 of the mounting construction.

Thus a vertical adjusting movement of the strut member 46 is effectively transferred through the member 94 and the strut to the actuating member 60 without appreciable ilexure of the switch arm 44 between the point of engagement of strut 46 therewith and lthe fitting 90. It should be noted that the flanges 54 on the arm or member S2 provide for a hinging movement of the arm at the region adjacent the mounting of the switch arm.

Through this construction the movement of the switch larm 52 under the bias of the spring 80 is transmitted to the contact 72 without appreciable iiexure of the flanged region of the switch arm 52. The edge regions of the arm 60 are formed with embossments or raised portions 114 extending throughout a substantial length of the central region of the arm 60 so that exure of the arm 60 occurs as 4a hinge action adjacent its mounting by the insulating washer 58.

It should be noted that the portion 68 or extension of the member 60 is a comparatively thin strip of flat or planar shape without any embossments so that this portion is readily flexed by movements of the thermoresponsive means 74 through engagement of the strut 88 with the portion 68 so that a transfer of bias through the spring 80 to the switch member 52 will be extremely sensitive and a snap action of the switch arm 52 attained by minute diiferentials in temperature.

The operation of the switch mechanism hereinbefore described is as follows: Assuming that the switch construction is embodied in a circuit arrangement for controlling an electrically energizable heating unit, an initial adjustment of the position of member 94 with respect to the switch arm 44 is made by rotating member 94 to establish an initial open position or spacing of the contacts 70 and 72. If a highly sensitive operation is desired, that is, wherein a separation of the contacts and the reestablishment of their engagement occurs in response to an extremely small temperature change, then the contacts are adjusted so that they are slightly out of engagement in open circuit position.

After such adjustment is attained by means of the member 94, readjustment need only be made when, it is desired to change the degree of sensitivity or a spacing of the contacts corresponding to an increased temperature lag or temperature differential defining the limits within which the thermoresponsive means is effective to engage and disengage the contacts 70 and 72. The extent of rotation of the shaft 36 between the limits prolwhich a unit controlled by the switch is to be maintained.

A calibrated dial (not shown) may be provided cooperating with an indicator on the knob 38 for setting the shaft 36 to the proper position. Through the threaded connection of the shaft 36 with the fitting Sti, the strut 46 is moved upwardly or downwardly depending upon the rotation of the shaft 36 to move the switch arm 44 to a predetermined position.

The unit 12 in circuit with the switch arms d4 and 52 becomes heated through engagement of the contacts 70 and 72 as the thermoresponsive means '74 is in its lowermost position so that the spring 8@ has biased the switch arm 52 into an upward or circuit closing position as shown in FIGURE 7. As the temperature increases in the region of the thermoresponsive means or bimetallic element 74, the element is exed upwardly so that the strut 83 carried at the distal end thereof engages the portion 68 of the actuating member 60 `and iiexes the portion 68 upwardly causing a rocking movement of the spring 80.

The projection 78 is moved through its critical position to a point at which the spring 80 exerts a biasing force eective to flex the distal end of the arm 52 in a downward direction by a snap action disengaging the contacts 70 and 72 to interrupt the circuit through the unit l2. This biasing force is eiective to maintain the contacts in separated position until the temperature is reduced adjacent the thermoresponsive means 74. As the thermoresponsive means is reduced in temperature, it is flexed downwardly as viewed in FIGURE 1 and the strut 88 moves downwardly in a direction away from the portion 68 of the arm 60.

This action permits the projection 78 to move downwardly through its critical position. When it reaches a point below this critical position, a biasing force through the spring 80 iiexes or moves the switch arm 52 upwardly with a snap action to again reestablish engagement between the contacts 70 and 72 completing the circuit through the heating or energized unit l2.

Hence the automatic action of maintenance of the temperature of the unit l2 continues and the only deviation from a constant temperature is the thermal differential or temperature difference required to rock the spring 89 and modify the direction of the biasing force through the spring acting upon the arm 52.

The switch means is particularly adapted for controlling air-'conditioning apparatus. To adapt the switch for such purpose, the bimetallic element is reversed so that an increase in temperature adjacent the bimetallic element causes it to flex in a direction to close the contacts and energize the air-conditioning apparatus and to flex in the opposite direction when the temperature is reduced to effect a separation of the contacts and interruption of the circuit to the air-conditioning apparatus,

It is apparent that, within the scope of the invention, modiiications and different arrangements may be made other than as herein disclosed, and the present disclosure is illustrative merely, the invention comprehending all variations thereof.

I claim:

l. Apparatus of the character disclosed, in combination, switch mechanism including a support, a first switch member, a second switch member, an end of each of said switch members being secured to the support, cooperating contacts carried by said switch members for controlling a circuit, an actuating member secured to the support and having a projection spaced from the distal end of said second switch member, an arcuately shaped spring having its end regions articulately engaging respectively the end of the second switch member and the pro- '3 jection of the actuating member to exert a biasing force on the second switch member in a direction dependent upon the relative position of the actuating member, means responsive to temperature variations arranged to iniiuence the position of said actuating member, an element supported on said first switch member, a strut formed 4of insulating material positioned between and engaging said element and the actuating member, said element being adjustable for regulating the position of the actuating member relative to the first switch member to control the space ybetween said contacts when the latter are in open circuit position.

2. Apparatus of the character disclosed, in combination, switch mechanism including a support, a rst switch member, a second switch member, an end of each of said switch members being secured to the support, cooperating contacts carried by said switch members for controlling a circuit, manually operable means for regulating the relative position of said first switch member, an actuating member having one end region secured to the support and the other end spaced from the distal end of said second switch member, an arcuately shaped spring having its end regions engaging respectively the ends of the second switch member and the actuating member and adapted to exert a biasing force on the second switch member in a direction dependent upon the relative position of the actuating member, and means responsive to temperature variations arranged to influence the position of said `actuating member, a fitting supported on said iirst switch member, a threaded element carried by said fitting, a strut formed of insulating material positioned between and engaging said element and the actuating member, said element being rotatable relative to said iitting for regulating the position of the actuating member with respect to the iirst switch member to control the space between said contacts when the latter are in disengaged relation.

3. Apparatus of the character disclosed, in combination, switch mechanism including a support, first and second switch arms formed of flexible material, one end of each of said switch arms being secured to the support, cooperating contacts carried by said switch arms for controlling a circuit, manually operable means for regulating the relative position of said irst switch arm, an actuating member having one end secured to the support and the other end spaced from the distal end of said second switch arm, said actuating member having a portion spaced from the distal end of the second switch arm, means responsive to temperature variations and movable to actuate said actuating member, an arcuately shaped resilient element having its end regions pivotally associated with the distal end of the second switch arm and the said portion of the actuating member whereby movements of the actuating member cause said arcuately shaped element to exert a biasing force upon said second switch arm to engage or disengage said contacts dependent upon the direction of movement of the actuating arm, said :first and second switch arms having embossments formed thereon at regions spaced from the support whereby iiexure of the switch arms occurs at regions adjacent the support, a fitting secured to said irst switch arm, means carried by said fitting and adjustable relative thereto and engageable with the actuating member for adjusting the space between said contacts when the latter are in disengaged relation to regulate the degree of sensitivity of the resilient element to open and close said contacts.

4. Apparatus of the character disclosed, in combination, switch mechanism including a support, irst and second switch arms formed of flexible strip material, one end of each of said switch arms being secured to the support, cooperating contacts carried by said switch arms for controlling a circuit, manually operable means for regulating the relative position of said iirst switch arm, an actuating member having one end secured to the support and the other end spaced from the distal end of said second switch arm, said actuating member having a projection extending toward and spaced from the distal end of the second switch arm, a bimetallic member having one end secured to the support, said bimetallic element extending substantially coincident with the actuating member, an element of insulating material disposed between the bimetallic element and the actuating member, said bimetallic element being responsive to temperature variations and movable to actuate said actuating member, an arcuately shaped resilient element having its end regions pivotally associated with the distal end of the second switch arm and the projection on the actuating member whereby movements of the actuating member cause said arcuately shaped element to exert a biasing force upon said second switch arm to engage or disengage said contacts dependent upon the direction of movement of the actuating arm, said iirst and second switch arms having embossments formed thereon at regions spaced from the support whereby ilexure of the switch arms occurs at regions adjacent the support, a fitting secured to one of said switch arms, a member carried by said iitting and adjustable relative thereto, and a strut member of insulating material disposed between the member carried by said iitting and the actuating member for adjusting the space between said contacts when the latter are in disengaged relation for adjusting the degree of sensitivity of the arcuately shaped member 80 for opening and closing said contacts.

5. Apparatus of the character disclosed, in combination, a tubular support member, a plate secured to said tubular member, first and second switch arms formed of exible strip material, one end of each of said arms being insulatingly supported upon said tubular member, an actuating means formed of flexible material having one end supported upon said tubular member, cooperating contacts mounted respectively on said irst and second switch arms and adapted to control an electrically energizable unit, a manually movable shaft mounted upon said plate, insulating means disposed between said shaft and said iirst switch arm whereby relative movement of said shaft influences the position of said rst switch arm whereby said rst switch arm may be adjusted to a position corresponding to a temperature setting of said manually operated shaft at which it is desired to maintain a predetermined temperature by control of the electrically energizable unit, said actuating means having a projection adjacent the end of said second switch arm, a curved spring disposed between the end of the second switch arm and the projection on the actuating member and adapted to exert a biasing force upon the second switch arm to obtain snap action movements thereof dependent upon relative movements of the actuating member, a bimetallic element having a portion supported adjacent said tubular member and coextensively disposed relative to said actuating means, insulating means carried by said bimetallic element and adapted for engagement with the actuating means whereby iexure of the bimetallic element responsive to temperature variations influences movement of said actuating member to positions whereby a biasing force is exerted upon the second switch arm through said curved spring in a direction dependent upon the position of said actuating means, means including an adjustable element disposed between said iirst switch arm and the actuating means for determining the initial spacing between said contacts when the latter are in disengaged position to regulate the sensitivity of movement of the second switch arm, said trst and second switch arms and said actuating member having flange portions formed thereon throughout a portion of the lengths of said switch arms and actuating member whereby tlexure of the switch arms occurs adjacent the mounting thereof and exure of the actuating member occurs adjacent the region of the curved spring.

6. Apparatus of the character disclosed, in combination, a tubular supporting member, a plate secured to said tubular member, first and second flexible switch arms, one end of each of said arms being insulatingly supported upon said tubular member, an actuating member having one end insulatingly supported upon said tubular member, cooperating contacts mounted respectively on said first and second switch arms and adapted to control an electrically energizable unit, a manually rotatable shaft mounted upon said plate, insulating means disposed between said shaft and said iirst switch arm, the rotation of said shaft being adapted to influence the position of said rst switch arm whereby said first switch arm may be adjusted to a position corresponding to a temperature setting of said manually operated shaft, a curved spring disposed between the end of the second switch arm and said actuating member and adapted to exert a biasing `force upon the second switch arm to 0btain a snap action movement of said second switch arm dependent upon relative movements of the actuating member, a flexible bimetallic element supported adjacent said tubular member, insulating means carried by said bimetallic element and adapted for engagement with the actuating member whereby flexure of the bimetallic element under the iniluence of temperature variations moves said actuating member to positions whereby a biasing force is exerted upon the second switch arm through said curved spring in a direction dependent upon the position of said actuating member, means disposed between said first switch arm and the actuating member for determining the initial spacing between said contacts when the latter are in disengaged position to regulate the sensitivity of the second switch arm to movement under the biasing force transmitted through the curved spring, said rst and second switch arms and said actuating member having ange portions formed thereon throughout a portion of the lengths of said switch arms and actuating member whereby flexure of the switch arms occurs adjacent the mounting thereof and exure of the actuating member occurs adjacent the region of the curved spring.

References Cited in the file of this patent UNITED STATES PATENTS 1,108,320 Berdon Aug. 25, 1914 2,515,528 Rothwell July 18, 1950 2,691,082 Turner et al. Oct. 5, 1954 

